1. Field of the Invention
This invention relates to an apparatus for forming the external leads of a semiconductor device.
2. Description of the Related Art
FIG. 1 shows a conventional type of lead forming apparatus. A hydraulic cylinder 104 is secured to the top of a housing 105 and a piston rod 103 of the hydraulic cylinder 104 is inserted through the housing 105. An upper plate 101a is fixed to the inserted end of the piston rod 103. A lower plate 102a is secured to a partitioning plate 106 which partitions the interior of the housing 105 into upper and lower compartments. An upper mold half 101, such as a punch, and a lower mold half 102, such as a die, are attached to the upper plate 101a and the lower plate 102a, respectively, opposed to each other. An upper stop 107 and a lower stop 108 are attached to the upper plate 101a at a location adjacent to the upper mold half 101 and the lower plate 102a at a location adjacent to the lower mold half 102, respectively, opposed to each other. A hydraulic unit 109 is disposed at the bottom of the housing 105 and is connected to the hydraulic cylinder 104 through hydraulic lines 110.
The operation of the above-described conventional lead forming apparatus will be described below. First, a leadframe (not shown) is located on the lower mold half 102. A semiconductor chip has been mounted on this leadframe, and the semiconductor chip and a portion of the leadframe have been encapsulated in a resin. Then, fluid is supplied from the hydraulic unit 109 to the hydraulic cylinder 104 through the lines 110, thereby causing the piston rod 103 with the upper mold half 101 to move downwardly. The downward movement of the upper mold half 101 severs a predetermined portion of the leadframe carried on the lower mold half 102, and thus the external leads of the semiconductor device are formed. The downward movement of the piston rod 103 is stopped when the upper stop 107 attached to the upper plate 101a comes into contact with the lower stop 108 attached to the lower plate 102a. More specifically, the bottom dead center of the piston rod 103 is determined by the upper stop 107 and the lower stop 108. Subsequently, the piston rod 103 is moved upwardly by the hydraulic unit 109 so that the upper mold half 101 is moved away from the lower mold half 102 and the semiconductor device finished as a product is removed from the lower mold half 102.
In such a conventional lead forming apparatus, however, since the downward movement of the piston rod 103 and the upper mold half 101 is stopped by pressing the upper stop 107 against the lower stop 108, a large impact occurs during the operation of the lead forming apparatus and, therefore, noise cannot be avoided.
If it is desired to form the external leads of semiconductor devices of different types, both the upper mold half 101 and the lower mold half 102 need to be replaced with mold halves suitable for use in forming the individual types of semiconductor devices. Upon replacement, the bottom dead center of the piston rod 103 must be adjusted according to the height of each of the upper and lower mold halves 101 and 102 which have been newly set on the lead forming apparatus. However, since adjustment of the bottom dead center of the piston rod 103 is carried out by replacing at least one of the upper and lower stops 107 and 108 with another stop of different height, much time is required to adjust it and precise adjustment is difficult to achieve.